The teaching according to the present invention relates to an improvement in and extension of the teaching disclosed in DE-A1 43 24 474 and in earlier German patent application P 44 28 269.9 relating to the surface stabilization of sand and/or soil--hereinafter also referred to as soil. These documents describe modifications of the process known per se for securing at least temporary stabilization by application and introduction of selected aqueous polymer preparations to and into the surface of soil layers susceptible to erosion. The water present in the impregnating agent introduced dries in a comparatively short time and the polymer phase left behind stabilizes the granular and/or clay-like structure of the impregnated soil without unduly affecting the permeability of these layers to water. The surface stabilization in question is not confined to soil in the narrower sense. The corresponding stabilization of other surface regions which have to be protected against wind erosion, for example, is also encompassed by the teaching according to the invention. Examples of such surface regions include rubbish dumps and/or waste tips with or without a covering of topsoil or other protective layers. However, grass-covered areas for example, which are exposed to fairly severe mechanical and/or climatic influences, are also susceptible to erosion. Examples of corresponding grass-covered areas are to be found in leisure facilities, such as golf courses with their well-trodden fairways and tees, fields for ball games, such as football, handball and the like. Grassed surfaces such as these are often susceptible to the well-known "dry spots" which are more vulnerable to the effects of weathering. Similar problems are also caused, for example, by wet, heavily compacted soil or by the formation of so-called "thatch" which prevents water applied from reaching the root layer and, hence, leads to the formation of undernourished dry areas which in turn become the starting point for erosion.
Development and practice have been concerned for decades with the concept on which the present invention is also based of applying synthetic polymers capable of bonding particulate solids to one another to the surfaces to be stabilized in the form of aqueous dispersions or emulsions and drying them on those surfaces in such a way that the stabilized soil is guaranteed adequate permeability to water. Particular practical significance is attributed in this regard to aqueous polyvinyl acetate dispersions (also referred to hereinafter as PVAc dispersions), cf. for example A. Kullmann et al. in Arch. Acker-Pflanzenbau Bodenkd., 22(11), 713-19. In addition to polyvinyl acetate, the following are described as useful binders: butadiene/styrene latex, a urea/formaldehyde polymer and a bitumen emulsion. The corresponding stabilization of dune sand against the effects of rain is the subject of an article by D. Gabriels et al. (Univ. Ghent, Belgium) in Soil Sci., 118(5), 332-8. This publication also mentions a binder system based on polyvinyl acetate among the preferred binders. So far as the other works carried out worldwide are concerned, reference is made purely by way of example to certain patents, cf. U.S. Pat. Nos. 4,072,020, 3,887,506, HU 11 654 and ZA 7501787.
The list of requirements and problems involved in soil stabilization is extremely diverse. Without any claim to completeness, many of the properties required in practice are listed in the following: the material should be resistant at least to pedestrian traffic; it should not be affected by the particular temperatures prevailing, by atmospheric moisture or by rain (for the particular period of time envisaged); it should also be resistant to high wind speeds. The material to be applied should be non-inflammable and should not represent a fire risk or exposure risk during storage and also during and after use. Its transport and application should not require any particular safety measures or the wearing of protective clothing. The cured polymeric impregnation should not have any toxic effects on germinating plants, on growing plants or on animals and should be colorless and transparent. Taking these and other requirements into consideration, the knowledge acquired hitherto may be summarized as follows:
1. PVAc homopolymer dispersions are basically suitable as binders. In the absence of plasticizers, however, they lead to such brittle cohesion of the impregnated layers of soil that crucial performance requirements are not satisfied. PA0 2. The deficiency mentioned in (1) can be overcome by adding plasticizers which are liquid under normal conditions. In practice, dibutyl phthalate in particular has established itself as a plasticizer. Although correspondingly plasticized PVAc homopolymers lead to firm cohesion, dibutyl phthalate is not degradable. By contrast, DE 43 24 474 discloses degradable plasticizers. PA0 3. Although internally plasticized polymer dispersions (polyvinyl acetate-co-dibutyl maleate) provide for firm cohesion, they are also non-degradable.
The teaching of DE-A1 43 24 474 cited at the beginning addresses the problem of providing PVAc homopolymer dispersions for the described application with plasticizers which, on the one hand, satisfy the various technical requirements but which, on the other hand, are biocompatible and, in particular, can be degraded. The teaching of this document is based on the knowledge that, basically, PVAc homopolymers are biocompatible and degradable even though the degradation of this polymer is comparatively slow. The relevant literature is represented, for example, by H. Kastien et al. "Der quantitative mikrobiologische Abbau von Lackkunstharzen und Polymerdispersionen", farbe+lack, Vol. 98, 7/1992, 505-8. According to the teaching of the cited document, the following selected classes of compounds are used as biologically acceptable plasticizers for PVAc dispersions: triesters of glycerol with lower aliphatic monocarboxylic acids, citric acid triesters with lower aliphatic monohydric alcohols and/or epoxidized triglycerides of at least partly olefinically unsaturated fatty acids.
Earlier German patent application P 44 28 269.9 likewise cited at the beginning relates to an improvement in the teaching of the document mentioned in the preceding paragraph. This improvement takes into account the fact that the soil surfaces stabilized with esters based on polyvinyl alcohol can soften up considerably where the substratum or underlying soil is wet or in the event of intensive contact with moisture, for example in the form of heavy rain. Although the stabilization generally returns after drying, i.e. does not completely disappear, there is nevertheless a weakness here so far as practical application is concerned. Accordingly, the earlier application cited relates to the use of fatty acids or fatty alcohols which are solid at room temperature and/or which cure on contact with air and/or at least substantially water-insoluble esters, ethers and/or salts thereof as degradable and biologically compatible stabilizers for increasing the resistance to water of soil impregnations based on polyvinyl acetate and comparable esters of polyvinyl alcohol with lower monocarboxylic acids. The disclosure of this earlier application is hereby included as part of the disclosure of the present invention, the key parameters which are now also to be used in the context of the new technical teaching being discussed in detail in the following.
The teaching according to the invention seeks to achieve a further improvement in the surface impregnation and stabilization of soil layers susceptible to erosion. A particular objective in this regard is to make it possible to influence the rate and, optionally, depth of penetration of the aqueous preparations containing the polymeric binders into the surface of the soil to be stabilized. In particular, the teaching according to the invention seeks to achieve sufficiently rapid and sufficiently deep penetration of the surface-stabilizing binder into the soil, even in problem areas, for example hillsides, heavily compacted soils or grassed areas affected by thatch and comparable inhibiting layers. At the same time, the teaching according to the invention seeks to achieve improved stabilizing effects--possibly even with less binder.
The teaching according to the invention is based on a concept which is already discussed in earlier German patent application P 44 28 269.9, namely the possibility of using small quantities of selected components resembling wetting agents in character in the aqueous preparations of the binder (impregnating agent) and/or the stabilizers. Surface-active components of the o/w type are described as being particularly suitable; in the preferred embodiment, they are also distinguished by their biological compatibility and, in particular, by their biological degradability. The class of surfactants based on alkyl polyglycosides (APG) is mentioned as one important example in this regard.
The technical teaching of the new development described in the following is based on the observation that the specifically controlled use of these and other surface-active wetting agents can optimize the required soil stabilization in many respects.